#Write an efficient program to find the double factorial of k written as k!!.
import sys
import time
f=open('in1_5.txt','r')
n=int(f.readline())
f.close()
t1=time.clock()
def fac(n):
    global no_mul
    if(n<=3):
        return n
    fact= n*fac(n-2)
    no_mul=no_mul+1
    return fact
no_mul=0
fact=fac(n)
t2=time.clock()
t=t2-t1
mem=sys.getsizeof(fact)+sys.getsizeof(no_mul)+sys.getsizeof(n)
f1=open('out_15_sec1_5.txt','w')
f1.write("%d!!=%d \nno. of multiplications=%d \ntime taken="%(n,fact,no_mul))
f1.write(str(t))
f1.write("seconds\nmemory used=%d bytes"%mem)
f1.close()